“Aayu and his half-sister Nandita were wonderful, confident and energetic calves, who loved nothing more than playing with the rest of the family herd—whether in the sand or the pool,” Mike Jordan, the director of animals at the zoo, said in a statement.

“They will be missed by their young siblings in the herd who will no doubt mourn for a short time. To lose them both is also devastating to all of us here who have cared for them day in, day out. It is just heartbreaking.”

The deaths come just weeks after Aayu’s mother Sithami, 20, died. The cause of death for Sithami has not been revealed publicly.

A zoo spokesperson told Metro that blood transfusions, a new attempt at treating EEHV, were attempted for the baby elephants but were ultimately unsuccessful.

“A team of expert scientists, conservationists, keepers, and vets worked tirelessly to administer anti-viral drugs to help the young elephants to fight the illness. The team also performed ground-breaking elephant blood transfusion procedures to help their immune systems fight back. Despite the exhaustive efforts, their conditions rapidly declined and both calves passed away this morning,” the spokesperson said.

EEHV

The herpesvirus affects elephant’s quickly and there’s no known vaccine or cure. It’s often fatal.

Researchers at the Smithsonian National Zoo in Washington said they were the first to identify the disease in 1995 after it killed a 16-month-old Asian elephant there.

“Elephants in human care and in the wild have been affected by EEHV, which has been responsible for about half of the deaths of young elephants in zoos. In response, cooperative multi-institutional research efforts have been underway for more than a decade to study EEHV, identify the various strains, learn about their transmission, develop and improve treatments, and find a vaccine,” the Smithsonian said.

If the diagnosis and treatment are early then elephants can recover, with a current success rate of a new anti-viral treatment of about 40 percent.

While the disease is primarily in zoos, it also affects elephants in the wild, with cases identified in India and Cambodia.